Injection-mold clamping unit having alternately ejecting die assemblies

ABSTRACT

An injection mold includes a stationary platen carrying a pair of stationary die sections, a movable platen carrying a pair of movable die sections, and a pair of floating die sections disposed between the movable and stationary die sections. The respective floating and stationary die sections are mutually configured to define a pair of die cavities which are arranged for alternate communication with an injector unit. The floating die sections are selectively connectable to their associated movable and stationary die sections to expose one of the die cavities for article ejection, while maintaining the other die cavity closed for continuing a curing stage.

This is a division of application Ser. No. 372,955, filed June 25, 1973,now U.S. Pat. No. 3,898,030.

BACKGROUND AND OBJECTS OF THE INVENTION

This invention relates to article molding, particularly whereinplasticated material is injected into a die cavity and allowed to cureto a desired degree before being removed.

Injection molding techniques for forming plastic and rubber articles arewell known. One such technique utilizes a clamping unit having astationary die section and a movable die section. Opposing faces ofthese die sections are configured to define a die cavity when thesections are in abutting relationship. The stationary die section isprovided with a sprue opening which communicates the interior of the diecavity with an injector unit capable of injecting a charge ofplasticated substance into the die cavity.

A suitable type of injector unit may be of the reciprocal screw type. Insuch a unit, a screw is rotated within a barrel to melt and mix apredetermined charge of material, such as plastic or rubber for example.Subsequently, the screw is reciprocated, in the manner of a piston, toram or "shoot" this charge through the sprue and into the die cavity.

Extremely high pressures are produced by such an injection operation. Toresist these pressures, a heavy-duty clamping unit is provided to urgethe die sections into tight interengagement. In many instances, theamount of counterforce or "clamp tonnage" necessary to maintain the diesections closed may be on the order of at least 20,000 psi, thusrequiring the use of clamps of substantial size.

After being injected into the die cavity, the plasticated chargesolidifies and may be subjected to a curing stage. Following this, thedie sections are separated, and the molded article is suitably ejected.

While such apparatus is capable of producing articles of high quality,the quantity of articles which may be produced thereby is somewhatrestricted, due mainly to the inactivity of the apparatus during thecuring stage. The extent of this inactivity varies somewhat, dependingupon the type of articles being molded. For example, in the productionof large automobile body or bumper components, from synthetic rubbermaterial, the period of inactivity may last for six minutes or more,during which time only a single article is being produced.

An effort to increase production, as by mounting a plurality of die pairon the platens to be injected simultaneously and cured simultaneously,would require the use of a larger injector in order to produce asufficiently large charge for injecting two die cavities simultaneously.Moreover, the injection pressures required to be resisted by the clampduring this simultaneous injection would increase substantially, therebyrequiring the use of much larger clamping apparatus.

It is, therefore, a general object of the invention to provide novelmethods and apparatus for obviating or minimizing problems of the sortpreviously noted.

It is a particular object of the invention to provide such novel methodsand apparatus which maximize the production rate of an injection-moldclamping unit while minimizing the required clamp tonnage.

It is another object of the invention to provide such novel methods andapparatus which maximize the production rate of an injection-moldclamping unit while minimizing the required clamp tonnage and injectorcapacity.

It is yet another object of the invention to provide such novel methodsand apparatus which enable a charge to cure in the clamp unitsimultaneously with the ejection of a cured charge therefrom.

BRIEF SUMMARY OF A PREFERRED EMBODIMENT

A preferred form of the invention intended to accomplish at least someof the foregoing objects entails an injection-mold clamping unit havinga plurality of die assemblies. Each die assembly includes a pair of diesections configured to define a die cavity when urged together. Lockingmechanism is provided to lock together the die sections of one dieassembly while the die sections of the other die assembly are beingseparated. Conversely, locking mechanism is provided to lock togetherthe die sections of another die section while the die sections ofanother die assembly are being separated.

More particularly, the clamping unit comprises stationary and movableplatens. Actuating mechanism is provided for shifting the movable platentoward and away from the stationary platen. A pair of die assemblies areprovided, each of which a stationary die section carried by thestationary platen, and a floating die section disposed intermediate themovable and stationary die sections. The floating and stationary diesections of each die assembly have opposed faces which are mutuallyconfigured to define a die cavity when in abutting relationship.Coupling mechanisms are mounted on the die assemblies and are operableto couple each floating die section with a selective one of itsassociated movable and stationary die sections.

The stationary die sections are provided with sprue openings whichcommunicate the die cavities with a material-injecting apparatus,preferably an injector unit of the reciprocal screw type. Communicationof the die cavities with the injector is alternated such that the diecavities may be injected independently at staggered intervals.

In a method aspect of the invention, the die assemblies are operated ina out-of-phase relationship. Thus, with the clamp closed, the injectorinjects melt into the die cavity of a first of the die assemblies, whilepreviously-injected melt cures in the die cavity of a second of the dieassemblies.

When curing of the latter is complete, accomplished to a desired degree,the clamp is opened, with the floating and movable die sections of thesecond die assembly being coupled together, to expose the die cavitythereof. The molded article is ejected therefrom. During this procedure,the floating and stationary die sections of the first die assembly aremaintained in coupled relationship to enable the melt therein to cure.

Subsequent closing of the clamp enables the second die cavity, nowempty, to be injected with a new charge of melt.

When the melt in the first die cavity has cured to a desired degree, theclamp is opened, with the floating and movable die sections of the firstdie assembly being coupled to expose the molded article for ejection.Simultaneously, the floating and stationary die sections of the seconddie assembly are coupled together to enable the melt therein to cure.

In this fashion, the production rate of the clamp is maximized, whilethe tonnage requirements of the clamp and the size of the chargerequired to be produced by the injector are minimized.

THE DRAWING

Other objects and advantages of the present invention will becomeapparent from the subsequent detailed description thereof in connectionwith the accompanying drawing in which like numerals designate likeelements, and in which:

FIG. 1 is a side elevational view, partly in longitudinal section, of aninjection-mold clamping unit, according to the invention, in one stageof its operational cycle;

FIGS. 2 and 3 are views similar to that of FIG. 1 depicting the clampingunit in other stages of operation;

FIG. 4 is a longitudinal sectional view of a die assembly taken alongline 4--4 of FIG. 3;

FIGS. 5 through 8 are views similiar to that of FIG. 1 depicting furtheroperational stages of the clamping unit;

FIG. 9 is a longitudinal sectional view of a portion of a die assemblyduring an ejecting stage, taken along line 9--9 of FIG. 8;

FIGS. 10 and 11 are views similar to that of FIG. 1 illustratingadditional stages of operation of the clamping unit;

FIG. 12 is a longitudinal sectional view of a portion of a die assembly,taken along line 12--12 of FIG. 1;

FIG. 13 is a schematic illustration, in perspective, of a pair of dieassemblies in accordance with one stage of clamp operation; and

FIG. 14 is a schematic view of a fluid circuit for actuating couplingcylinders of the clamping unit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referred to FIG. 1, a preferred form of an injection-mold clamping unit10 comprises a stationary frame or platen 12 and a movable frame orplaten 14. The movable platen 14 is slidably mounted on a plurality ofstrain rods 16, preferably four in number, which project outwardly fromthe stationary platen 12.

Projecting rearwardly from the movable platen 14 are a plurality ofcompression columns 18, the function of which is to be subsequentlydescribed.

Adjacent their outer ends, the strain rods fixedly carry a back plate 20having openings 22 which accommodate sliding movement of the compressioncolumns 18 therethrough.

Mounted on the back plate 20 is a fluid-actuated traverse cylinder 24,the rod end of which is attached to the movable platen 14. Extension ofthe traverse cylinder 24 causes the movable platen 14 to be shiftedtoward the stationary platen 12.

The back plate 20 has mounted thereon a fluid-actuated lock cylinder 26,the rod end of which carries a lock plate 28. The lock plate 28 includesa pair of locking legs 30 which straddle the traverse cylinder 24.Disposed in each of the locking legs 30 are a pair of apertures 32 whichmay be selectively aligned with the openings 22 in the back plate 20.The lock cylinder 26 is operable to slide the lock plate 28 between acolumn-unlock position and a column-lock position. In the column-unlockposition, the apertures 32 are aligned with the openings 22 toaccommodate sliding movement of the compression columns 18 (FIG. 1). Inthe column-lock position, the locking legs 30 are disposed to cover theopenings 22 (FIG. 3).

Each strain rod 16 is movably mounted relative to the stationary platen12. A power mechanism is provided to exert clamping leverage to hold thedie cavities closed. A preferred form of power mechanism comprises afluid-actuated main clamping cylinder 34, the piston 36 of which beingintegral with its associated strain rod. Each of the pistons 36 isslidably disposed within a chamber 38 in the stationary platen 12.Pressurized fluid may be fed to the rod side of this main clampingcylinder to retract the strain rods 16 in a manner shifting the backplate 20 toward the stationary platen 12.

Conversely, when pressurized fluid is supplied to the piston side of themain clamping cylinders, the strain rods 16 will be extended to shiftthe back plate 20 away from the stationary platen 12. In thisconnection, it is desired that pressurized fluid fed to the piston endof the main clamping cylinder be supplied to an auxiliary or break-awaycylinder 40 which is mounted on the piston 36. This break-away cylinder40 is reciprocally mounted in an auxiliary chamber 42 which isconsiderably smaller than the chamber 38.

Operably associated with the clamp is an injector unit for supplying acharge of plasticated material, such as rubber or plastic for example.

One suitable form of injector 44 is of the reciprocal screw type. Suchinjector 44 typically includes a barrel 46 having a discharge orifice 48at one end thereof and a plasticator screw 50 rotatably and reciprocallymounted in the barrel 46. Motors for rotating and reciprocating thescrew within the barrel (not shown) are also provided in the usualmanner.

In operation, forward rotation of the screw 50 causes plastic or rubberstock material within the barrel to be advanced and melted in a knownfashion. With the discharge orifice being blocked by a conventionalblocking device, the plasticated material, or melt, tends to accumulateat the tip of the barrel, and the screw 50 is rearwardly displacedwithin the barrel 46. After the screw 50 has receded by a predetermineddistance, the orifice 48 is unblocked and the screw is reciprocatedforwardly to ram the melt through the orifice and into die portions ofthe clamp.

The main clamping cylinders 34 are designed to resist the injectionpressures imposed on the clamp during this melt-ramming operation.

As described to this point, the clamping unit comprises conventionalelements capable of operating in a known manner. Heretofore, thestationary and movable platens have each been provided with a single diesection, which together define a die cavity when in abuttingrelationship. With the clamp closed, melt is injected into the diecavity. Subsequently, the die sections are held tightly shut while themelt cures. During this time, the injector is operated to prepareanother charge of melt. In many instances, a fresh charge is preparedwell prior to the end of the curing stage. However, the initiation of asubsequent injection operation must be delayed until the melt has curedto a desired degree.

In accordance with this invention, however, a plurality of dieassemblies are provided which enable the clamp and extruder to beutilized in the production of a second article, while theinitially-injected charge cures.

Although any suitable number of die assemblies may be employed inconjunction with the clamp, the preferred embodiment utilizes a pair ofside-by-side die assemblies 52A and 52B. If so desired, however, the dieassemblies could be vertically superposed.

The die assemblies 52A, B, include stationary die sections 54A and 54B,movable die sections 56A and 56B, and floating die sections 58A and 58B.

The stationary die sections 54A, B are fixedly secured to the stationaryplaten 12. Opposing or proximate faces 60 and 62 of the stationary andfloating die sections are mutually configured to define die or moldcavities 64A and 64B there between (FIG. 7). These die cavities areshaped in accordance with the desired configuration of articles intendedto be produced thereby. Sprue channels 66A and 66B are provided in thestationary die sections 54A, B. These sprue channels are arranged tocommunicate the die cavities 64A, B with the extruder 44, via channels68A and 68B.

Suitable mechanism is provided for initially directing melt from theinjector 44 to one of the die cavities 64A, B. Preferably, thismechanism is in the form of a sprue plug 70 which is configured to seatwithin and block a sprue opening (FIG. 1). In this fashion, when theplug 70 is inserted within the sprue opening of one of the die cavities,the flow of melt thereto will be blocked and diverted to the other diecavity.

If desired, however, a suitable valving arrangement could be employed inthe passages 68A, B, in lieu of the plug 70, to selectively divert themelt flow.

The movable die sections 56A, B are fixedly secured to the moving platen14 for reciprocal movement there with toward and away from theassociated stationary die sections 54A, B.

The floating die sections 58A, B are disposed between the stationary andmovable die sections. Preferably, these floating die sections eachinclude a plurality of guide pins 72 which project toward alignedrecesses 74 and 76 carried by the associated stationary and movable diesections (FIG. 12.)

The floating die sections 58A, B are arranged to be alternately coupledto their associated movable and stationary die sections 54A, B and 56A,B. Suitable apparatus for accomplishing this comprises fluid-actuatedcoupling cylinders 78A, 78B, 80A, and 80B (FIGS. 1, 13, and 14). Thesecoupling cylinders are preferably mounted on the stationary and movabledie sections by means of suitable brackets 82 (FIG 9), although theycould be attached to the floating die sections if so desired.

Each coupling cylinder includes a locking dog 84 carried at the end ofthe rod portion of the cylinder. Each locking dog has a tapered recess86 which is engagable with lugs 88 situated on opposite sides of each ofthe die sections. The tapered recesses of the locking dogs are operableto engage converging surfaces of these lugs when the die sections aredisposed in abutting relationship. The wedge-like configuration of therecesses 86 enables the coupling cylinders to hold their associated diesections in tight interengagement when the cylinders are in a couplingposition.

By alternately actuating the coupling cylinders associated with each ofthe die assemblies 52A, B, the floating die sections 58A, B may besequentially couples to their associated stationary and movable diesections 54A, B, and 56A, B. A hydraulic fluid circuit such as thatdepicted in FIG. 14, is preferably utilized for this purpose. Thiscircuit includes a pump P for supplying hydraulic fluid under pressurefrom a reservoir R. A sleeve valve 90 is provided and is selectivelyactuable to conduct pressurized fluid to the piston sides of either theset of 78A and 80B or the set of coupling cylinders 80A and 78B toextend the locking dogs 84 thereof. Simultaneously, the valve directspressurized fluid to the rod ends of the other set of coupling cylindersto retract the locking dogs associated therewith.

By coupling together the movable and floating die sections, the diecavities associated therewith may be exposed by withdrawing the movableplaten 14 from the stationary platen 12. In this fashion a cured articledisposed in the cavity may be displaced therefrom.

An article-ejecting mechanism is desirably employed to displace curedarticles.

One suitable form of article-ejecting mechanism, shown particularly inFIG. 9, comprises a stationary plate 94 which is fixedly secured to theclamp in any suitable manner (not shown). Preferably, the stationaryplate 94 is located between the movable platen 14 and the back plate 20.A plurality of ejector pins 96 project forwardly from the stationaryplate 94. These ejector pins 96 are aligned with apertures 98, 100 and102 located in the movable platen 12, the movable die sections 56A, B,and the floating die sections 58A, B.

Within each aperture 102 of the floating die sections 58A, B is slidablydisposed a push-out rod 104. These rods 104 extend through the floatingdie sections and terminate in enlarged head portions 106. The rods 104are biased rearwardly by compression springs 108 to a position in whichthe head portions 106 are seated within recesses 110 of the floating diesections so as to be contiguous with the outer faces of the floating diesections.

When the movable platen 12 is shifted toward the stationary plate 94,the ejector pins 96 pass through the apertures 98 and 100 and depressthe rod 104 forwardly to eject cured articles 112 adhering to thefloating die sections.

OPERATION

According to the invention, the die assemblies 52A and 52B are operatedin a out-of-phase relationship. A molding operation may be initiated byshifting the sleeve valve 90 to a position in which pressurized fluid isdelivered to the piston ends of the coupling cylinders 78A and 80B andthe rod ends of the coupling cylinders 78B and 80A (See FIG. 14).Consequently, the locking dogs 84 carried by the cylinders 78A and 80Bwill be extended to couple together the floating and stationary diesections 54A and 58A of the die assembly 52A, as well as the floatingand movable die sections 58B and 56B of the die assembly 52B.

Subsequent retraction of the traversing cylinder 24 will separate thefloating and stationary die sections 58B and 54B, thereby exposing thedie cavity 64B (See FIG. 1). In this position, the floating die section58B is effectively carried by the movable die section 56B by means ofthe guide pins 72 which are disposed in the apertures 76 of the movabledie section 56B.

The plug 70 is inserted into the sprue opening 66B to blockcommunication between the die cavity 64B and the injector unit 44.

At this point, the traversing cylinder 24 is extended to its full extentto shift the movable platen 14 toward the stationary platen 12 (See FIG.2). In this fashion, the floating and stationary die sections 58B and54B of the die assembly 52B are brought into closely adjoiningrelationship, i.e., within a fraction of an inch of closing the diecavity 64A.

At this stage of operation, the ends of the compression columns 18 willbe spaced sufficiently from the lock plate 28 to enable the lockcylinder 26 to slide the locking legs 30 to a position wherein theycover the openings 22 (See FIG. 3).

Pressurized fluid is subsequently delivered to the main clampingcylinders 34 to shift the strain rods 16, the back plate 20, and thelock plate 28 toward the stationary platen 12. As a result the legs 30of the lock plate 28 engage the ends of the compression columns 18 andforcefully urge the floating die sections 58A, B tightly against thestationary die sections 54A, B to develop tonnage.

During the foregoing procedure, the injector 44 has functioned toprepare a charge of melt. Accordingly, when the main clamping cylinders34 have been actuated to firmly clamp the floating and stationary diesections, the screw 50 is reciprocated forwardly within the barrel 46 toinject the melt through the orifice 48. Since the sprue 66B is blockedby the plug 70, the melt will be diverted through the sprue 66A and intothe die cavity 64A. The injection forces produced by this operation areeffectively resisted by the clamp tonnage imparted to the die assembliesby the main clamping cylinders 34. When the die cavity 64A has beenfilled with melt, the orifice 48 is blocked and the melt begins a curingstage. The injector 44 is immediately actuated to produce a fresh chargeof melt.

While the fresh charge is being prepared, pressurized fluid is fed tothe break-away cylinders 40 to initially separate the floating diesection 58B from the stationary die section 54B (See FIG. 5).Subsequently, the lock cylinder 26 is actuated to slide the lock plate28 to realign the apertures 32 and the openings 22. The traversingcylinder 24 is then retracted to fully withdraw the floating die section58B from the stationary die section 54B (See FIG. 6). The plug 70 is nowremoved from the sprue 66B.

During this clamp-opening procedure, the floating die section 58A andthe stationary die section 54A have been maintained in tight abuttingrelationship, since they are held together by the locking dogs 44 of thecoupling cylinders 78A. Thus, despite the fact that the clamp is in anopen condition, material within the die cavity 64A continues to cure.

With the plug 70 now removed the sprue 66B, the traversing cylinder 24,the lock cylinder 26, and the main clamping cylinders 34 aresequentially actuated to close the clamp 10 (See FIG. 7). When a freshcharge of melt is prepared by the injector, the screw 50 is reciprocatedforwardly to inject the melt into the die cavity 64B, the cavity 64Abeing occupied by the melt curing therein. Upon completion of thisinjection step, the orifice 48 is closed and the melt within the diecavity 64B begins to cure.

The clamp 10 is maintained in a closed position until the melt disposedin the die cavity 64A has cured to the desired degree. At this point,the floating die section 58A may be separated from the stationary diesection 54A to expose the molded article. Subsequent to the reclosing ofthe clamp and prior to the separation of the floating and stationary diesections 58A and 54A, the spool valve 90 is shifted to communicate thepump P with the piston ends of the coupling cylinder 80A and 78B. Inthis fashion, the floating die section 58A will be coupled to themovable die section 56A, and the floating die section 58B will becoupled to the stationary die section 54B.

The clamp is now opened by initially directing pressurized fluid to thebreak-away cylinders 40. This produces sufficient break-away tonnage torelease the forces on the compression columns 18. The lock cylinder 26is now actuated to realign the apertures 32 with the openings 22, andthe traversing cylinder 24 is retracted to fully withdraw the floatingdie section 58A from the stationary die section 54A (See FIG 8).

When the movable platen 12 reaches its fully withdrawn position, theejector pins 26 will enter the apertures 98 and 100 and will depress theejector rods 104, as shown in FIG. 9. As a result, the enlarged headportions 106 of the rods 104 will displace the cured article 112 fromthe floating die section 58A.

During the reopening of the clamp 10, the floating and stationary diesections 58B and 54B are held together by the coupling cylinders 58B toenable the melt disposed within the die cavity 64B to cure.

The clamp is now closed by suitable actuation of the traversing cylinder24, the lock cylinder 26, and the main clamping cylinders 34.

When a fresh charge has been prepared by the injector 44, it is ejectedthrough the orifice 48. Since the die cavity 64B contains a charge, theinjected melt will be diverted to the die cavity 64A, as shown in FIG.10.

Subsequent to the filling of the die cavity 64A, both die cavitiesremain closed until the charge in the die cavity 64B has cured to thedesired degree. With the hydraulic circuit of the coupling cylinderssuitably actuated to couple together the floating and stationary diesections 58A and 54A, as well as the floating and movable die sections58B and 56B, the clamp 10 is opened in the same manner as previouslydiscussed to expose the die cavity 64B. When the movable platen 12reaches its fully withdrawn position, the ejector pins 96 depress theejector rods 104 in the floating die section 58B to eject the curedarticle 112, as shown in FIG. 11.

From this point, the molding cycle is continued from the stage describedin connection with FIG. 1. It will be appreciated, however, that thereis no longer a need for a sprue plug 70, since the curing chargesdisposed within the die cavities will function to suitably divert meltwhich is discharged from the injector 44.

As will be apparent from the foregoing discussion, the production rateof the multi-die clamp according to this invention is greater than thatof a conventional single-die clamp. Significantly, this advantage isaccomplished without necessitating increases in either clamp tonnage orinjector capacity requirements.

Accordingly, the injector need only be of a size sufficient forproducing charges of melt to inject a single die cavity.

Hence, neither the tonnage requirements of the clamp nor the chargecapacity of the injector are increased.

Specifically, since the die cavities are injected independently andsince the power cylinders 34 are common to the die assemblies, the clampis required to develop tonnage sufficient to resist pressuresaccompanying the injection of only one die cavity.

Since during the curing and ejecting stages of an initially-injectedcharge, the clamp receives and partially cures a second charge, theproduction rate of the clamp will be significantly increased.

Although the invention has been described in connection with a preferredembodiment thereof, it will be appreciated by those skilled in the artthat additions, modifications, substitutions and deletions notspecifically described may be made without departing from the spirit andscope of the invention as defined in the appended claims.

What is claimed is:
 1. In molding apparatus of the type in whichmaterial is injected into die cavity means and allowed to remain in saiddie cavity means for an interval, and then the molded material isremoved from the die cavity means, the improvement comprising:astationary platen; a movable platen movable toward and away from saidstationary platen, a plurality of die assemblies each including afloating die section and an associated stationary die section, theproximate faces of which being configured so as to define therebetween amold cavity;said stationary die sections being mounted on saidstationary platen; connecting means releasably connecting said floatingdie sections to said movable platen, and releasably connecting saidfloating die sections to said associated stationary die sections; powermeans operatively associated with said movable platens for moving saidmovable platen away from said stationary platen to:separate the diesections of one of said die assemblies whose floating die section isreleased from its associated stationary die section and connected tosaid movable platen, and move away from another of said die assemblieswhose floating die section is disconnected from said movable platen andconnected to its associated stationary die section, and injector meanscommon to a plurality of die cavities of said die assemblies so as to beselectively communicable therewith for selectively injecting materialtherein;said injector means including a stationary barrel having anoutlet, and conduits communicating said outlet with said stationary diesections of said plurality of die cavities.
 2. A molding apparatuscomprising:a stationary platen; a movable platen; first and secondmovable die sections mounted on said movable platen; first and secondstationary die sections mounted on said stationary platen; first andsecond floating die sections respectively disposed between said firstand second movable and stationary die sections;said first floating andstationary die sections and said second floating and stationary diesections respectively defining first and second die cavities when inabutting relationship; a plurality of first fluid-actuated couplingcylinders carried by said first die sections;one of said first couplingcylinders being actuable to a coupling posture to couple said firstfloating die section with said first movable die section; another ofsaid first coupling cylinders being actuable to a coupling posture tocouple said first floating die section with said first stationary diesection; a plurality of second fluid-actuated coupling cylinders carriedby said second die sections;one of said second coupling cylinders beingactuable to a coupling posture to couple said second floating diesection to said second movable die section; another of said secondcoupling cylinders being actuable to a coupling posture to couple saidsecond floating die section to said stationary die section; a pluralityof guide rods carried by at least one of each of said first and seconddie sections;said guide rods being receivable in apertures carried by atleast an adjacent one of each of said first and second die sections; aninjector unit, having rotatable and reciprocal screw means,communicating with said first and second die cavities;said screw, inresponse to forward rotation thereof, being operable to advance andplasticate molding material, and screw, in response to forwarddisplacement thereof, being operable to inject plasticated material intoalternate ones of said first and second die cavities; fluid-actuatedclamp cylinder means operatively associated with said movable platen forselectively moving said movable platen toward and away from saidstationary platen to urge said first and second floating die sectionsinto firm abutting relationship with their associated first and secondstationary die sections and close said first and second die cavities;and ejector means for displacing a molded article from said die cavitieswhen the latter are exposed;with said die cavities being closed by saidclamp cylinder means, and with access to said first die cavity beingblocked by material curing therein, said extruder is operable to injectextrudate into said second die cavity; with said one of the firstcoupling cylinders, and said other of the second coupling cylinders,being in a coupling posture, said clamp cylinder means is operable toseparate said first floating and stationary die sections to expose saidfirst section for ejection by said ejector means, while material in saidsecond die section cures; and with said other of the first couplingcylinders, and said one of the second coupling cylinders being in acoupling posture, said clamp cylinder means is operable to separate saidsecond floating and stationary die sections to expose said second diecavities for ejection by said ejector means, while material in saidfirst die cavity cures.
 3. A molding apparatus comprising:stationaryframe means; movable frame means; at least two die assemblies, each dieassembly including a pair of die sections;each pair of said die sectionsbeing arranged to define a cavity when in abutting relation; said diecavities being operable to receive a charge of plasticated material;injector means communicating with said die cavities for selectivelyinjecting material therein; power means, common to said die assemblies,forexerting force to simultaneously clamp together the die sections ofsaid die assemblies during insertion of a charge of plasticatedmaterial, and releasing such clamping force simultaneously from the diesections of said die assemblies; said movable frame means being commonto said die assemblies and being arranged to transmit clamping forcesfrom said power means simultaneously to said die assemblies; saidstationary frame means carrying one of the die sections of each of saiddie assemblies so that such carried die sections constitute stationarydie sections; the other die section of each die assembly beingdisplaceable relative to said stationary die sections so as toconstitute floating die sections; means for coupling a floating diesection of one of said die assemblies to said movable frame means whenthe die sections of said last-named die assembly are rendered relativelydisplaceable; maintaining means, including means coupling the floatingdie section of one of said die assemblies to its respective stationarydie section, maintaining the die sections of said one of said dieassemblies in abutting relationship while the die sections of anotherdie assembly are rendered relatively displaceable, when said power meansis in a force-releasing mode; and maintaining means, including meanscoupling the floating die section of said other die assembly to itsrespectively stationary die section, maintaining the die sections ofsaid other die assembly in abutting relationship while the sections ofsaid one die assembly are rendered relatively displaceable, when saidpower means is in a subsequent force-releasing mode.
 4. A moldingapparatus comprising:at least two die assemblies, each die assemblyincluding a floating die section and a stationary die section;each ofsaid floating and stationary die sections being arranged to define a diecavity when in abutting relation; injector means communicating with saiddie cavity for injecting a charge of plasticated material into said diecavity power means, common to said die assemblies, forexerting force tosimultaneously clamp together the floating and stationary die sectionsof said die assemblies to resist injecting forces, and releasing suchclamping force simultaneously from the floating and stationary diesections of said die assemblies; means maintaining the floating andstationary die sections of one of said die assemblies in abuttingrelationship, while the floating and stationary die sections of anotherdie assembly are rendered relatively movable, when said power means isin a force-releasing mode; and means maintaining the floating andstationary die sections of said other die assembly in abuttingrelationship while the floating and stationary die sections of said onedie assembly are rendered relatively movable, when said power means isin a subsequent force-releasing mode.
 5. A molding apparatus accordingto claim 4 wherein said injecting means comprises an injector unitcommon to said die cavities to supply plasticated material to alternateones thereof.
 6. A molding apparatus according to claim 4 and furtherincluding movable frame means, common to said die assemblies, arrangedto transmit clamping forces from said power means simultaneously to saiddie assemblies; and means for coupling said floating die section of oneof said die assemblies to said movable frame means when the die sectionsof said last-named die assembly are rendered relatively movable.
 7. Amolding apparatus according to claim 6 and further including stationaryframe means carrying said stationary die sections of each of said dieassemblies.
 8. A molding apparatus according to claim 7 wherein saidmaintaining means comprises at least one fluid-actuated locking cylinderassociated with each of said die assemblies, said cylinder including anextendable and retractable locking dog for engaging and releasingportions of said floating and stationary die sections.
 9. A moldingapparatus according to claim 8 wherein said movable frame means includesa further pair of die sections associated with said pair of dieassemblies, said further pair of die sections constituting movable diesections; the locking cylinders being carried by said movable andstationary die sections and having tapered recesses in the locking dogsthereof for engaging tapered lug portions of said die sections.
 10. Amolding apparatus according to claim 9 wherein each die assembly furtherincludes guide rod means carried by at least one of said die sections;said projection means projecting toward and being receivable in aperturemeans carried by at least an adjacent die section.
 11. The moldapparatus of claim 10 wherein said guide rod means comprises a pluralityof guide rods carried by said floating die section and being receivablein apertures carried by said movable and stationary die sections.
 12. Inmolding apparatus of the type in which material in injected into diecavity means and allowed to remain in said die cavity means for aninterval, and then the molded material is removed from the die cavitymeans, the improvement comprising:first and second frame membersarranged for relative movement toward and away from one another; atleast first and second die assemblies disposed between said first andsecond frame members in side-by-side relation so as to be spaced in adirection transverse to the direction of relative movement between saidframe members;each die assembly including a mating die section and afloating die section, the proximate faces of which being configured soas to define therebetween a closed mold cavity when said die sectionsare disposed in abutting relation;said floating die sections beingmovable relative to one another; the mating die section of each dieassembly being carried by one of said first and second frame members;injector means communicating with said mold cavities of said first andsecond die assemblies for selectively injecting material therein;coupling means coupling said floating die sections selectively to eitherof said frame members to the exclusion of the other frame member;saidcoupling means being arranged, while coupling a floating die section tothe frame member which carries the mating die section associated withsaid last-named floating die section, to lock said die sections togetherin abutting relationship so as to maintain said mold cavity closed; andpower means operatively associated with said frame members for movingsaid frame members relatively toward and away from one another suchthat:with said floating die section of said first die assembly beingcoupled to said one frame member and uncoupled from said other framemember, and with said floating die section of said second die assemblybeing coupled to said other frame member and uncoupled from said oneframe member, separation of said frame members by said power meanscauses the mold cavity of said second die assembly to be opened forremoving material therefrom, with the mold cavity of said first dieassembly being maintained in a closed condition for retaining materialtherein; and with said floating die section of said first die assemblybeing coupled to said other frame member and uncoupled from said oneframe member, and with said floating die section of said second dieassembly being coupled to said one frame member and uncoupled from saidother frame member, separation of said frame members by said power meanscauses said mold cavity of said first die assembly to be opened forremoving material therefrom, with said mold cavity of said second dieassembly being maintained closed for retaining material therein; andwith said first and second frame members being moved toward one anotherso that said first and second mold cavities are clamped closed by saidpower means, an empty one of said mold cavities may be supplied withmaterial while material being carried by the other mold cavity cures.13. Molding apparatus according to claim 12 wherein said mating diesections are mounted so as to be stationary.
 14. A molding apparatuscomprising:first and second relatively movable frame means; a first dieassembly including a pair of die sections arranged to define a closedfirst die cavity when in abutting relationship, said closed die cavitybeing operable to hold a charge of plasticated material;one die sectionof said first die assembly comprising a first mating die section carriedby one of said frame means; the other die section of said first dieassembly comprising a floating die section capable of being;coupled tosaid one frame means carrying said first mating die section anduncoupled from the other frame means wherein said first mating diesection and said first floating die section are in abutting relationshipto define said closed first die cavity, and coupled to said other framemeans and uncoupled from said one frame means carrying said first matingdie section so as to be out of abutting relationship with said firstmating die section such that said first die cavity is opened forejecting cured material therefrom; a second die assembly including apair of die sections arranged to define a closed second die cavity whenin abutting relationship, said closed second die cavity being operableto hold a charge of plasticated material;one die section of said seconddie assembly comprising a second mating die section carried by one ofsaid frame means; the other die section of said second die assemblycomprising a second floating die section capable of being:coupled tosaid one frame means carrying said second mating die section anduncoupled from the other frame means wherein said second mating diesection and said second floating die section are in abuttingrelationship to define said closed second die cavity, and coupled tosaid other frame means and uncoupled from said one frame means carryingsaid second mating die section so as to be out of abutting relationshipwith said second mating die section such that second die cavity isopened for ejecting cured material therefrom; said first floating diesection being movable relative to said second floating die section;injector means communicating with said first and second die cavities forselectively injecting material therein; power means operativelyassociated with said frame means for:shifting said first and secondframe means relatively toward one another such that said die sections ofsaid first and second die assembly are clamped in abutting relationship,said power means being arranged to exert sufficient clamping force toresist forces occurring during the insertion of plasticated materialinto one of said die cavities, and shifting said first and second framemeans to a separated position; coupling means being arranged, with saidfirst and second frame means being in a separated positionfor:maintaining said first floating die section coupled to the framemeans carrying said first mating die section and uncoupled from theother frame means, wherein said first die cavity is closed to allowuncured material therein to cure, and simultaneously maintaining saidsecond floating die section uncoupled from the frame means carrying saidsecond mating die section and coupled to the other frame means so thatsaid second die cavity is opened for the removal of cured materialtherefrom; and said coupling means being further arranged, with saidfirst and second frame means being in a subsequent separated position,for:maintaining said first floating die section uncoupled from the framemeans carrying said first mating die section and coupled to the otherframe means sso that said first die cavity is opened for the removal offcured material therefrom, and simultaneously maintaining said secondfloating die section coupled to the frame means carrying said secondmating die section and uncoupled from the other frame means, whereinsaid second die cavity is closed to allow uncured material therein tocure.
 15. Molding apparatus according to claim 14 wherein said first andsecond mating sections are disposed between said first and second framemeans in side-by-side relation so as to be spaced in a directiontransverse to the direction of relative movement between said framemeans.
 16. Molding apparatus according to claim 15 wherein said firstand second mating die sections are mounted so as to be stationary. 17.Molding apparatus according to claim 14 wherein said first and secondmating die sections are mounted so as to be stationary.